The fuel tank access doors used so far to gain access into the fuel tanks in the wings of aircraft, for inspection, present manufacturing and operational difficulties. Since the wings of aircraft are three-dimensionally curved, at least in its bottom skin where the fuel tank access doors are located, and since the wings are dynamic members undergoing twisting and bending movements in flight, the metal doors used so far have to be carefully machined. There has resulted that the fuel tank access doors used so far have been rather expensive to make particularly since such doors have to be leakproof despite all the aforementined adverse requirements. Another disadvantage of those metal doors is that they cannot readily be made of sheet metal and their manufacturing cost is therefore rather high. This is particularly noticeable since each aircraft is provided with a plurality of such fuel tank access doors.